Process for spinning elastic polypropylene fibers



United States Patent No Drawing. Filed July 10, 1963, Ser. No. 294,198US. Cl. 264210 13 Claims Int. Cl. D01d 5/12 This invention relates topolypropylene fibers and more particularly polypropylene fibers havingelastic properties and their method of manufacture.

Fibers having good elastic properties along with other requisitephysical properties such as toughness, abrasion resistance and stabilityhave previously been prepared from normally elastic materials such asrubber and polyurethane. It has also been known to produce semielasticmaterials by mechanically treating normally non-elastic fibers bymethods such as crimping and crinkling in order to provide a slightdegree of elasticity.

Previous to the present invention however, it has not been possible tophysically treat a normally nonelastic polymer during fiber formationand subsequent thereto to produce a truly elastic filament out of anormally nonelastic polymer. It has also previously not been possible toproduce a truly elastic fiber out of a polymer as cheap and plentiful aspolypropylene.

It is therefore an object of the present invention to produce a fullyelastic and inexpensive polypropylene fiber.

It is another object of the present invention to produce an elasticpolypropylene fiber using standard synthetic fiber production machinery.

It is another object of the present invention to provide a novel processfor producing an elastic polypropylene fiber.

It is another object of the present invention to produce a polypropylenefiber With elastic properties at rates commensurate with normalsynthetic fiber production on standard equipment.

It is another object of the present invention to produce elasticpolypropylene staple yarn.

Other objects and the nature and advantages of the instant inventionwill be apparent from the following description thereof.

The production of the elastic polypropylene fibers is dependent onnumerous int-errelating processing variables. In general, however,elastic polypropylene fibers will not be obtained unless thepolypropylene resin is melt extruded at a temperature lying betweenabout 325 and 500 F. and at a jet velocity of below about 40 feet perminute, then stretched to produce a draw-down ratio of between about 60and 300 to 1, then heat-set in a relaxed state, and finallydraw-oriented an amount between about 1.01 and 2X at a temperaturebetween the second order transition and about 316 F.

According to the present invention, the selected polypropylene is placedin a conventional screw extruder and is therein reduced to a melt. Thepolypropylene is then melt-extruded at a constant extrusion rate jetvelocity of between about 1 and 40 feet per minute. The filamentsissuing from the die are Wound up at rates higher than normal (e.g.,sufiicient to produce a draw-down ratio of between 60 and 300 to 1).This may be accomplished by extruding the polypropylene filamentsdownwardly into a quench bath or other cooling medium (e.g., air) andaround wind-up rolls which stretch the polypropylene filaments from thedie by rotating at about 60' to 300 times the jet velocity. The fibersmay then be draw-oriented without any external application of heat(e.g., at room temperatures) or up to 316 F. with heat and theoreticallyas low as the second order transition temperature of the 3,432,590Patented Mar. 11, 1969 resin. Either a single or multiple stage drawingis effective. Subsequent to orientation (if a first orientation isperformed) the material is heat-set in a relaxed state to produceelastic fibers. A cold draw-orientation after heatsetting is essentialin order to reduce the force required to elastically deform the fibers,and must be effected to an amount between about 1.01 and 2x at atemperature between the second order transition and about 316 F.

If desired, staple filaments may be produced. After the firstorientation, following the procedure above, the filaments are crimpedaccording to normal well known procedures. The crimped filaments may bethen either heatset or cut to the desired staple length since heatsetting may be done in either the tow, staple, or spun yarn form.Similarly, the second orientation step, i.e., after the heat setting,may be done in tow or spun yarn form.

The propylene polymers suitable for the present invention are anypolypropylene resins with fiber forming properties. Resins having lowand high melt indices of 0.3 to 500 have been utilized to produceelastic fibers according to the present invention. Such resins areavailable commercially. It has been found, however, that when using meltindices above about it is desirable to blend these polymers with smallamounts of polymers having a lower melt index in order to permitorientation at room temperature or below.

In carrying out the present invention the poly-propylene is melted andextruded at temperatures of 325 F. to 550 F. through spinnerets in anotherwise well known manner, thereby forming the extrudates orfilaments. The filament size is dependent upon the size of the spinneretorifice and the degree of draw-down. For instance, a filament may bereduced to about 1/60 to 1/ 300 of its initial extruded thickness as itis stretched from the die and passed into a quench bath. Afterheat-setting under relaxed conditions, which causes a slight increase indiameter, the filament is reduced approximately to its preheat-setdiameter in draw-orienting.

In actual operation the hot melt is extruded into filaments which passthrough a quench bath maintained at room temperature or below. Thefilaments are taken up on a fixed speed take-up roll. The filaments arethen either heat-set under relaxed conditions or cold-drawn (oriented)by having a second take-up roll travelling at a fixed but more rapidspeed, e.g., up to 2 times faster than the first one. In between thesetake-up rolls the filaments may pass through a gaseous medium in a tubemaintained at room temperature preferably, but which may lie anywherebetween the second order transition temperature and 316 F.

Heat-setting, which may be effected either after orienting or directlyafter wind-up stretching (thus obviating a first cold-draw), is carriedout by passing the filaments through a roll travelling at a fixed rate,then passing the filaments through a heated zone (e.g., an oven, aheated tube, infrared heaters, etc.) and finally through another rolltravelling at a reduced rate. The speed of the roll following the heateris set by the amount of shrinkage of the filaments so that the filamentsare heated in the absence of tension but without allowing the filamentsto accumulate in a bunch before passing through the roll. Heat-settingmay also be effected by passing the filaments through a heated mediumwhile they lie relaxed on a conveyor belt. If desired, the heat-settingmay be carried out in a plurality of stages.

After heat-setting the filaments must then be cold-drawn (oriented) asdescribed above. This orientation may also be conducted in a pluralityof stages with the fibers in tow or spun yarn. If desired, the filamentsmay be woven into fabric and then cold-drawn in this form eitheruniaxially or biaxially.

Extruder temperatures should be low enough to prevent high rates ofresin thermodegradation and this will be determined by the extruderdesign, the molecular Weight of the resin and the through-put rate. Thelowest stock temperature is the temperature at which the resin melts.This will be higher for low melt index resins (high molecular weights).The average melting point for polypropylene is approximately 325 F. Thehigher the molecular weight, the lower will be the temperature ofthermodegradation. The higher the through-put rate, the higher will bethe rate of shear which causes a build-up in temperature. Generally, thelower the amount of thermal degradation in the extruder, the better theelastic properties.

Orientation should be conducted at room temperature. Theoretically, thelowest effective temperature would be at the second order transitiontemperature for polypropylene and the highest effective temperaturewould be approximately 316 F. or where crystal formation is promoted.The orientation ratio should be great enough to produce an opaque hue atroom temprature in an unpigmented fiber. The opacity is presumably dueto molecular stress and displacement of crystal structure. Normalhot-orientation according to the prior art would require the fiber to beheated to about 285 F. with a heated plate or oven mounted between theorienting rolls and the amount of draw would be greater than 2 X Forproducing the elastic properties the fiber should be heat set in arelaxed state at a temperature great enough to remove the opaque hue ofthe fiber. Removing the opaque hue can be accomplished at 200 F. for 30seconds and, in fact, using longer intervals, can be accomplished atmuch lower temperatures although for practical purposes the temperatureshould be no lower than about 180 F. It is most desirable, however, touse a higher temperature since the heat-setting can then be accomplishedfaster. The most desirable temperatures have been found to be 265 F. to295 F. At 295 F. the shrinkage is approximately to 12 percent of theoriginal (cold-oriented) length (when, of course, a first cold-draw isused). If the filaments are heat-set directly after hot-stretching, theshrinkage is less than 5%.

EXAMPLE I A polypropylene resin having a melt index of 5 was melt-spunat 430 F. at a rate of 19 lbs. per hour (to produce a filament of 15denier per filament). The jet velocity was 16.8 ft. per minute. Thetake-up rate was 2400 ft. per minute. The resultant filaments wereoriented at room temperature, heat-set at 200 F. for 30 seconds underrelaxed conditions and then stretch-oriented a Second time. Each stretchorientation was 2X. The resultant filament was elastic.

EXAMPLE II A polypropylene resin having a melt index of 5 was extrudedat lbs. per hour to provide filaments having 15 denier per filament. Thestock temperature was 430 F. and the jet velocity was 17.7 ft. perminute. The take-up speed was 2400 ft. per minute. The count at thetake-up was approximately 17 denier per filament. After a 2X coldorientation followed by heat-setting and a second cold orientation, anelastic filament having 15 d.p.f. was produced.

As a control, a conventional 15 d.p.f. filament was produced as follows:

A polypropylene having a melt index of 5 was extruded at the rate of 20lbs. per hour (jet velocity 16.7 ft. per minute) at a stock temperatureof 590 F. and a take-up speed of 580 ft. per minute. The d.p.f. attake-up was 75. The material was hot oriented 5 X to produce anon-elastic polypropylene filament having 15 d.p.f.

EXAMPLE III Polypropylene resin having a melt index of 5 was extruded ata rate of 5 lbs. per hour at a stock temperature of 430 F. to produce anelastic fiber of 15 d.p.f. The jet velocity was 2.3 ft. per minute. Inorder to produce such a fiber the take-up rate was 640 ft. per minute.

As above, orientation was conducted at room temperature and amount 2X.This was followed by heat-setting under relaxed conditions at 200 F. for30 seconds. This in turn was followed by a second orientation of 1.5

EXAMPLES IV-VI Examples IIII were repeated as above utilizing, in placeof the resin having a melt index of 5, a resin having a melt index of20. In addition, the extrusion temperature was reduced to 410 P. All theother variables remained constant. Examples IV-VI provided elasticfibers while a control for each, conducted as above, providednon-elastic fibers.

EXAMPLE VII A polypropylene resin having a melt index of was melt-spunat 410 F. at a rate of 9.5 lbs. per hour (jet velocity 17.5 ft. perminute) and was taken up at a rate of 2400 ft. per minute. Uponattempting to colddraw the filament to effect orientation it wasdiscovered that it was necessary to add heat. The filaments were heatedto F. and stretched. After heat-setting under relaxed conditions andreorienting, elastic fibers were produced.

EXAMPLE VIII A polypropylene resin having a melt index of 100 wasblended with 10% of a polypropylene resin having a melt index of 5. Thismaterial was formed into elastic filaments according to the conditionsset forth in Example VII above. This blend, however, permitted draworientation to be effected at room temperature.

EXAMPLE IX A polypropylene resin having a melt index of 100 was blendedwith conventional heat stabilizers and processed into elastic filamentsin accordance with the conditions set forth in Example VII above. Thisblend would not cold stretch at room temperature but required heating to150 F.

EXAMPLE X A polypropylene resin having a melt index of 100 was blendedwith 10% polypropylene having a melt index of 5 and with conventionalheat stabilizers. The conditions of Example VII were again carried outexcept that the take-up rate was 2200 ft. per minute. The filamentswould not cold stretch at room temperature and required heating to F.which produced elastic fibers.

EXAMPLE XI A resin having a melt index of 200 was blended with heat andUV stabilizers and pigment and was extruded at a temperature of 410 F.at a rate of 16.2 lbs. per hour. The jet velocity was 29.8 ft. perminute. The filaments were taken up at 2400 ft. per minute anddraworiented 2 at F. (the filaments resisted stretching at roomtemperature). After heat setting under relaxed conditions and a secondorientation, filaments having slightly elastic properties were produced.

EXAMPLES XIII-XV III Each of the conditions outlined above in ExamplesVII-XII were repeated except that the through-put was reduced to 5 lbs.per hour with a jet velocity of 2.3 ft. per minute and the maximumtake-up utilized was 640 ft. per minute. In each case an elasticfilament was EXAMPLES XIX-XXIV EXAMPLE XXV A polypropylene resin havinga melt index of 100 was extruded at 410 F. at the rate of 4.3 lbs. perhour, (jet velocity of 2.0 ft. per minute) with a 630 ft. per minutetake-up. The undrawn filament was heat-set for minutes at 295 F. in arelaxed state. A single stage orientation of 1.5 x was then applied tothe heat-set filament. The properties of this filament were thencompared as follows with standard commercially available filaments:

6 Elastic properties as extension:

P.S. 1.0 I.E.R. 76.8 D.R. 22.2 T.S.R 99.0

It will be obvious to those skilled in the art that various changes maybe made without departing from the spirit of the invention and thereforethe invention is not limited to what is described in the specification,but only as indicated in the appended claims.

I claim:

1. The method of forming elastic polypropylene filaments comprising (1)melt spinning high melt index polypropylene under low thermodegradationconditions and at a temperature between about 325 F. and 550 F. at a jetvelocity rate between about 1 and 40 ft. per minute, (2) stretching thefilaments at a high rate sutficient to produce a draw-down ratio ofbetween about and 300 to 1, (3) cold drawing the filaments less than 2Xto produce an opaque hue and to effect orientation, (4) heat setting thefilaments in a relaxed state, and (5) finally cold drawing thefilaments, to produce an opaque hue,

[Instron tests at 100% extension/minute] Percent Load Sample CountPounds SD. R3. I.E.R. D.R T.S.R at 15% Example XXV 1, 860/ 35. 0 0. 6660. 0 39. 3 99.3 0. 5 Nylon 6. 840/136 17. 9 1. 13 64. 6 34. 3 98. 9 l2.6 Non-elastic Polypropylen 2, 500/150 26.2 0. 70 73. 2 21. 5 99. 5 15. 54% Polyurethane in Orlou 440 41. 9 64. 0 13. 3 22.7 36.0 1. 4

ELASTIC PROPERTIES AT 50% EXTENSION (ELON GATION) [Instron tests atextension/minute] Percent Load Sample Count Pounds SD. R8. I.E.R. D.R.T.S.R. at 50% Example XXV 1, 860/70 41. 1 0. 8 78. 0 19. 2 97. 2 0. 68

STRESS-STRAIN VALUES [Instron tests at 200% extension/minute] UltimateUltimate Sample Count Elongation Tensile rength Example XXV. 0/70 230.0 1. 0 on- 840/ 18.0 8. 2 Non-elastic Polypropylene 2, 500/ 22. 0 5.0 4%Polyurethane in Orlon. 40 40. 0 2. 5 Polyurethane 70/1 490. 0 1. 5

sile Strain Recovery; all reported as percent of the applied stress.

EXAMPLE XXVI A polypropylene resin having a M.I. of 200 was blended witha 5 M.I. resin in a 90/10 weight-weight proportion with suitable heatand UV. stabilizers and also with a .45 concentration of crystallinepigments. The blended resin was extruded at 9.5 lb. per hour at a jetvelocity of 18.5 ft. per minute. The windup rate from the die was 2470ft. per minute. The undrawn fibers were heatset by passing through aheated oven (285 F.). Fiber residence time in the oven was approximatelyten seconds with an overfeed of 1.08:1. Total tow denier wasapproximately 100,000. The heat-set tow was then oriented in two stagesof 1.08:1 each. Physical properties of this tow were determined byweighing meter lengths of converting to denier per filament. The Instronstress-strain curve breaks at 100% extension per minute.

Tow denier 100,000 D.P.F. 6.0 U.E., percent 485 U.T.S. g./d 0.5

an amount between about 1.01 and 2 X at a temperature between roomtemperature and the lowest temperature at which the particular M.I.polypropylene can be stretched and substantially less than 285 F. toeffect orientation.

2. A method in accordance with claim 1 wherein said cold drawing iseffected at room temperature.

3. A method in accordance with claim 1 further comprising crimping saidfilaments after the first cold-draw and later cutting said filaments tostaple length and recombining said staple filaments into tow form priorto said final cold-draw.

4. A method in accordance with claim 3 wherein said cutting to staplelength precedes said heat-setting and said heat-setting is carried outon the staple filaments in tow form.

5. A method in accordance with claim 3 wherein said cutting to staplelength is after said heat-setting but before said final cold-draw.

6. A method in accordance with claim 3 wherein said cutting to staplelength is after said final draw-orientation.

7. A method in accordance with claim 1 wherein said heat-setting iseffected in a plurality of stages.

8. A method in accordance with claim 1 wherein said cold-draw is carriedout in a plurality of stages.

9. The method of forming elastic polypropylene fibers comprising (1)melt spinning the polypropylene under low thermodegradation conditionsat a temperature between 375 and 475 F. at a jet velocity rate betweenabout 1 and 40 ft. per minute, (2) hot stretching the filaments from thedie at a high rate sufiicient to produce a draw-down ratio of betweenabout 60 and 300 to 1, (3) cold drawing the filaments at roomtemperature an amount less than 2X to produce an opaque hue, (5)heat-setting the filaments in a relaxed state at temperatures greaterthan 180 F. and (5) cold drawing the filaments to produce an opaque hue,an amount between about 1.01 and 2X at room temperature.

10. A method in accordance with claim 17 wherein said polypropylene hasa melt-index of between 0.7 and 80.

11. A method in accordance with claim 1, further comprising forming afabric from said filaments after heatsetting and prior to cold drawing.

12. A method in accordance with claim 1 wherein said heat-setting iscarried out at 265-295 F.

13. A method in accordance with claim 1 wherein said orientation iscarried out at a temperature no greater than 150 F.

References Cited UNITED STATES PATENTS Compostella et al. 264-290Chantry et a1 264-210 Herrman 26421O Baratti 264-210 Martin 28172 Benson264210 Hebeler 264-168 Martin.

Gates.

Boltniew.

Tessien.

FOREIGN PATENTS US. Cl. X.R.

1. THE METHOD OF FORMING ELASTIC POLYPROPYLENE FILAMENTS COMPRISING (1)MELT SPINNING HIGH MELT INDEX POLYPROPYLENE UNDER LOW THERMODEGRADATIONCONDITIONS AND AT A TEMPERATURE BETWEEN ABOUT 325* F. AND 550* F. AT AJET VELOCITY RATE BETWEEN ABOUT 1 AND 40 FT. PER MINUTE, (2) STRETCHINGTHE FILAMENTS AT A HIGH RATE SUFFICIENT TO PRODUCE A DRAW-DOWN RATIO OFBETWEEN ABOUT 60 AND 300 TO 1, (3) COLD DRAWING THE FILAMENTS LESS THAN2X TO PRODUCE AN OPAQUE HUE AND TO EFFECT ORIENTATION, (4) HEAT SETTINGTHE FILAMENTS IN A RELAXED STATE, AND (5) FINALLY COLD DRAWING THEFILAMENTS, TO PRODUCE AN OPAQUE HUE, AN AMOUNT BETWEEN ABOUT 1.01 AND 2XAT A TEMPERATURE BETWEEN ROOM TEMPERATURE AND THE LOWEST TEMPERATURE ATWHICH THE PARTICULAR M.I. POLYPROPYLENE CAN BE STRETCHED ANDSUBSTANTIALLY LESS THAN 285* F. TO EFFECT ORIENTATION.